Hydrazine-bridged dinuclear

Preparation and X-Ray Structure of a Hydrazine-Bridged Dinuclear Molybdenum Complex [Mo(S2CN(C2H5)2)2(CO)2]2N2H4 CH2CI2... 

Kinetics and mechanisms of hydrazine-forming reactions, involving coupled redox and substitution processes, from dinitrogen-bridged dinuclear diethyldithiocarbamate complexes of niobium and tantalum have been reported and discussed. ... 

The high lability of bound N2 in [FeII(CN)5N2]3 regenerates the active site, namely the [FeII(CN)5H20]3 ion, which is able to further bind and process hydrazine. A more detailed kinetic study could be warranted for this interesting set of reactions. Some uncertainties still remain as to the nature of the intramolecular electron-transfer rate processes (91). At the employed concentration levels of the complex, the participation of mixtures of mononuclear and dinuclear complexes complicate the spectral evolution. Even the nature of the dinuclear intermediates (cyano- or hydrazino-bridged) could be put into question (probably both are involved, due to the labile interconversion equilibria). The participation of Fe(III) species, either in the mononuclear or dinuclear species, as reactive intermediate precursors of the formation of diazene and N2... 

In contrast Shilov and his group propose a very different mechanism (Scheme 20), which involves a bridging dinitrogen and four vanadium atoms, each acting as a one-electron reductant (contrasting to Schrau-zer s proposal that vanadium acts as a two-electron reductant). The hydrazine may then be reduced to ammonia. On theoretical grounds Shilov considers that dA metal ions would make the best dinitrogen reducers in these binuclear systems (44), and there is ample evidence to support the formulation of vanadium(II) dinuclear species in aqueous solution. However, Shilov postulates and finds vanadium(III) products, which Schrauzer ascribed to a conproportionation (289) as shown in Eq. (78). 

Dinuclear vanadium complexes with bridging diazenido(2—). The ligands are 2,6-bis(l-iminoethyl)pyridine (53)h h mesityl(l—) (54),h l 2-dimethylaminophenyl(l—) and pyridine (55),h l tolane, trimethylphosphine and dimethylamino-Cp(l—) (56),and benzamidinate(l —) (57).P 1 The complexes 54 and 55, containing (r-aUcyls, produce ammonia and hydrazine on protonation. 

An impure dinitrogen complex of niobium has been reported by Leigh et Complex 4 (see Table 1) is formulated as a dinuclear complex with a bridging dinitrogen. Treatment with acid yields no ammonia, but ca. 20% of the nitrogen is converted to hydrazine, the remainder being evolved as N2. 

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